I have 3 GPU's in my system and all of them are stock RX 470's.  While running it shows GPU 0, 1, and 2 all working fine.  The odd thing is when it shows the temperatures and fan speeds it will only show this for GPU 0 and GPU 1.  I have tried using -gmap 012 and also -gmap 210 and it still only shows 2 of the GPU's.  See below: